For proper spooling of a cable on a winch drum, it is necessary to keep a certain amount of tension on the cable for a neat, tight spool. When paying out cable from a drum it is necessary to keep tension on the line to prevent what is commonly called "birdcaging". This occurs when the winch drum pays out line faster than the line is retrieved or taken up.
One type of cable tensioner generally has one driven sheave and one or two idler sheaves with one or more pinch rollers to force the wire rope down into the sheave grooves causing a wedging action on the cable. To obtain the necessary friction area to lower the pounds per square inch force it is necessary to have an "S" curve cable lead to obtain the friction area required. These tensioners are required to handle the full line pull of the winch drum and must have sheave diameters proportionally larger than the cable diameter to avoid excessive bending of the cable.
Another type of tensioner presently utilized has compressible floating sides to the friction sheave along with a pinch roller to provide the necessary friction. Again it is necessary to have an "S" curve in the cable in the tensioner plus again having to handle the full winch load with the necessary large sheaves.
The two types described above cause constant bending, flexing and pinching of the wire rope causing premature failure of the cable.
Still another type of tensioner simply has the wire rope pinched in between two sheaves. In order to develop any appreciable amount of line pull it is necessary to place considerable pressure on the cable which then also results in premature cable failure.
Attention is directed to U.S. Pat. Nos. 4,469,267 and 2,647,699.
An object of this invention is to provide a cable tensioner which will maintain a constant tension on a cable without any bending, flexing or pinching of the cable.
Another object is to provide a tensioner which will follow the cable lead which means the structure does not change the direction of the cable lead (and load). It only has to support its own weight and some of the weight of the cable between the drum and the guide pulley. The tensioner must also handle the line pull under some conditions.